PHP Introduction to Server-Side Programming
Charles Liu
Request to a Static Site
Server: 1. Homepage lookup 2. Send as HTTP Response HTTP Request: GET www.xkcd.com
You (client)
Web server HTTP Response: web content (HTML file) Client-side code: HTML, CSS, JavaScript
IP: 72.26.203.99
Request to a Dynamic Site
The server must respond dynamically if it needs to provide different client-side code depending on the situation Date and time Specifics of the user’s request Database contents – forms and authentication Server: 1. Look up things that go on user’s profile, such as wall posts and friends caches, database lookups Web server 2. Generate client-side code containing these HTTP Response: web content (HTML file) things Client-side code: HTML, CSS, JavaScript 3. Send as HTTP response
HTTP Request: GET www.facebook.com
You (client)
(dynamically generated by server)
PHP Introduction and Basic Syntax
Charles Liu
What is PHP?
PHP = PHP: Hypertext Preprocessor Server-side scripting language that may be embedded into HTML Ultimate goal is to get PHP files to generate clientside code must
end up with HTML, CSS, JavaScript, other clientside code!
Side-by-side PHP File:
Output: resulting HTML
<html> <head> <title> PHP Introduction </title> </head> <body> This is HTML! <br /> <?php echo 'This is PHP! <br />'; ?> </body> </html>
<html> <head> <title> PHP Introduction </title> </head> <body> This is HTML! <br /> This is PHP! <br /></body> </html>
A closer look <html> <head>
<title> PHP Introduction </title> </head> <body> This is HTML! <br /> <?php echo 'This is PHP! <br />'; // prints to screen /* Here's a longer comment that spans multiple lines. */ ?> </body> </html>
PHP tags: <?php and ?> The echo command
Single line comment ( // ) Multiple line comment (/* and */)
Viewing PHP files
PHP files executed on the web server Therefore we cannot save them anywhere and view them, as with HTML files Must save .php files in subdirectory of web server /var/www/ on many Linux configurations www directory of your user directory on Athena
Make call to web server via domain name (google.com), IP address (72.26.203.99), or localhost if on your own computer
PHP Syntax: Variables, Operators, and Strings
Charles Liu
Variables
Store values for future reference, use variable name to refer to the value stored in it $x = echo echo $x =
42; // $x; // $x+1; // ‘hello!’ //
store the value 42 in $x prints 42 prints 43, value of $x is still 42 type of $x can change
PHP is a loosely-typed language Do
not need to declare the type of a variable Type can change throughout the program
Operators
Arithmetic operators +,
-, *, /, % (modulus – remainder after division)
Logical AND (&&), OR (||), NOT (!) Assignment operators Shorthand for assignment operators: += $y equivalent to $x = $x + $y Also works with subtraction, multiplication, division, modulus, and string concatenation $x
== versus ===
Two “equality” operators ==
tests for “equality” in value but not necessarily type === tests for “identity” in value AND type
== ignores the distinction between: Integers,
floating point numbers, and strings containing the same numerical value Nonzero numbers and boolean TRUE Zero and boolean FALSE Empty string, the string ‘0’ and boolean FALSE Any other non-empty string and boolean TRUE
Strings
A sequence of characters Single and double quotes: Suppose
$str = 42; echo ‘With single quotes, str is $str’;
output: With single quotes, str is $str
echo “With double quotes, str is $str”;
output: With double quotes, str is 42
Strings
Concatenation of strings – the . operator $a = ‘hello’; $b = ‘world’; echo $a . ‘ ‘ . $b . ‘!’;
// prints ‘hello world!’
String functions Length:
strlen() Position of substring: strpos() More on string functions: http://www.w3schools.com/php/php_ref_string.asp
PHP Syntax: Conditional and Looping Statements
Charles Liu
Conditional Statements if (condition / boolean expression) { statements } else if (another condition) { statements } // there may be more than one else if block else { statements }
$x = 5; if ($x == 5) { echo â&#x20AC;&#x2DC;The variable x has value 5!â&#x20AC;&#x2122;; }
The while loop while (condition) { statements } $x = 2; while ($x < 1000) { echo $x . “n”; // \n is newline character $x = $x * $x; } Value of $x
$x < 1000?
Result
2
TRUE
prints 2
4
TRUE
prints 4
16
TRUE
prints 16
256
TRUE
prints 256
65536
FALSE
exits loop
The do-while loop ď&#x201A;¨
The code within the loop is executed at least once, regardless of whether the condition is true do { statements } while (condition);
equivalent to: statements while (condition) { statements }
The for loop for (init; condition; increment) { statements }
equivalent to: init while (condition) { statements increment }
Prints the first 10 positive integers and their squares: for ($i = 1; $i <= 10; $i++) { echo $i . “:” . ($i * $i) . “\n”; }
PHP Syntax: Functions and Global Variables
Charles Liu
Defining your own functions function function_name ($arg1, $arg2) { function parameters function code return $var // optional }
Example: a simple multiply function function multiply($x, $y) { echo $x * $y; echo “\n”; } multiply(5, 1.2); prints 6 $a = 5; $b = 1.2; multiply($a, $b); prints 6 $a = array(1,2,3); multiply($a, $b); error $a = “string” multiply($a, $b); prints 0 (?!)
Return values
A function can return a value after it is done Use
this value in future computation, use like a variable, assign value to a variable
A modified multiply function
function multiply($x, $y) { return $x * $y; } multiply(2,3); prints nothing! returns value, but we don’t store anywhere echo multiply(2,3); prints 6 $a = multiply(2,3); assigns the value 6 to the variable $a $b = multiply(multiply(2,3), multiply(3,4)); assigns the value 72 to the variable $b
Return values
A function can return at most once, and it can only return one value
If it does not return anything, assignments will result in NULL
A function ends after it returns, even if there is code following the return statement
function do_stuff($x) { if ($x % 2 == 0) { // if even return $x/2 // exits function at this point } // this is ONLY executed if x is odd $x += 5; if ($x < 10) { $x += 3; } return x; }
Making function calls
Code inside of a function is not executed unless the function is called. Code outside of functions is executed whenever the program is executed. <?php … // some code function1();
// makes function call to function1(), which // in turn calls function3()
function function1() { … // some code function3(); } function function2() { … // some code } function function3() { … // some code } ?>
// makes function call to function3()
// this function is never called!
Variable scope
Variables declared within a function have local scope
Can only be accessed from within the function
<?php function function1() { … // some code $local_var = 5; echo $local_var + 3;
// this variable is LOCAL to // function1() // prints 8
} … // some code function1(); echo $local_var;
?>
// does nothing, since $local_var is // out of scope
Global variable scope
Variables declared outside a function have global scope
Must use global keyword to gain access within functions
<?php function function1() { echo $a; // does nothing, $a is out of scope global $a; // gain access to $a within function echo $a; // prints 4 } … // some code $a = 4; // $a is a global variable function1(); ?>
PHP Syntax: Arrays
Charles Liu
Arrays as a list of elements
Use arrays to keep track of a list of elements using the same variable name, identifying each element by its index, starting with 0
$colors = array(‘red’, ‘blue’, ‘green’, ‘black’, ‘yellow’);
To add an element to the array: $colors[] = ‘purple’;
To remove an element from the array: unset($colors[2]); $colors = array_values($colors);
Arrays as key-value mappings
Use arrays to keep track of a set of unique keys and the values that they map to – called an associative array
$favorite_colors = array(‘Joe’ => ‘blue’, ‘Elena’ => ‘green’, ‘Mark’ => ‘brown’, ‘Adrian’ => ‘black’, ‘Charles’ => ‘red’);
To add an element to the array: $favorite_colors[‘Bob’] = ‘purple’;
To remove an element from the array: unset($favorite_colors[‘Charles’]);
Keys must be unique: $favorite_colors[‘Joe’] = ‘purple’ overwrites ‘blue’
Recap: arrays
print_r($array_name) function lets you easily
view the contents of an array PHP arrays as a list
$colors = array(‘red’, ‘blue’, ‘green’, ‘black’, ‘yellow’); $colors[] = purple; // add to the list //remove ‘blue’ from list unset($colors[1]); $colors = array_values($colors);
PHP arrays as a map
$favorite_colors = array(‘Joe’ => ‘blue’, ‘Elena’ => ‘green’, ‘Mark’ => ‘brown’, ‘Adrian’ => ‘black’, ‘Charles’ => ‘red’); $colors[‘random person’] = ‘white’; unset($colors[‘Adrian’]);
PHP More about arrays and the for-each loop
Charles Liu
All arrays are associative
Take our example of a list:
$colors = array(‘red’, ‘blue’, ‘green’, ‘black’, ‘yellow’);
print_r($colors)
gives:
Array(
)
=> => => => =>
red blue green black yellow
Turns out all arrays in PHP are associative arrays
[0] [1] [2] [3] [4]
In the example above, keys were simply the index into the list
Each element in an array will have a unique key, whether you specify it or not.
Specifying the key/index
Thus, we can add to a list of elements with any arbitrary index Using
an index that already exists will overwrite the
value $colors = array(‘red’, ‘blue’, ‘green’, ‘black’, ‘yellow’); $colors[5] = ‘gray’; // the next element is gray $colors[8] = ‘pink’; // not the next index, works anyways $colors[7] = ‘orange’ // out of order works as well
Array functions
isset($array_name[$key_value])
tells whether a mapping
exists AND is non-null
removes the key-value mapping associated with $key_value in the array unset($array_name[$key_value])
The unset() function does not “re-index” and will leave gaps in the indices of a list of elements since it simply removes the key-value pairing without touching any other elements
and array_values($array_name) returns lists of the keys and values of the array array_keys($array_name)
Adding elements without specifying the key
Recall that we did not specify the key when adding to a list of elements: $colors = array('red', 'blue', 'green', 'black', 'yellow'); $colors[] = 'purple';
PHP automatically takes the largest integer key that has ever been in the array, and adds 1 to get the new key $favorite_colors = array(“Joe” => “blue”, “Elena” => “green”, “Mark” => “brown”, “Adrian” => “black”, “Charles” => “red”); $favorite_colors[] = 'new color 1'; // key is 0 $favorite_colors[7] = 'another new color'; $favorite_colors[] = 'yet another color'; // key is 8 unset($favorite_colors[8]); $favorite_colors[] = 'color nine'; // key is 9, the old // maximum is 8 even though it no longer exists!
The for-each loop ď&#x201A;¨
The for-each loops allow for easy iteration over all elements of an array.
foreach ($array_name as $value) { code here } foreach ($array_name as $key => $value) { code here } foreach ($colors as $color) { echo $color; // simply prints each color } foreach ($colors as $number => color) { echo â&#x20AC;&#x153;$number => $colorâ&#x20AC;?; // prints color with index // to change an element: // $colors[$number] = $new_color;
PHP HTTP Requests and Forms
Charles Liu
Superglobals
A few special associative arrays that can be accessed from anywhere in a PHP file Always $_ALLCAPS The $_SERVER superglobal gives information about server and client server IP $_SERVER[‘REMOTE_ADDR’] client IP $_SERVER[‘HTTP_USER_AGENT’] client OS and browser $_SERVER[‘SERVER_ADDR’]
Passing information to the server
Sometimes, we require additional values be passed from client to server Login:
username and password Form information to be stored on server
GET request: pass information via the URL http://www.yourdomain.com/yourpage.php?firstparam
=firstvalue&secondparam=secondvalue Access values server-side using $_GET superglobal $_GET[‘firstparam’]
=> ‘firstvalue’ $_GET[‘secondparam’] => ‘secondvalue’
When to use $_GET vs. $_POST
GET requests are sent via the URL, and can thus be cached, bookmarked, shared, etc GET requests are limited by the length of the URL POST requests are not exposed in the URL and should be used for sensitive data There is no limit to the amount of information passed via POST
Dealing with forms
Forms are generally used to collect data, whether the data needs to be stored on the server (registration) or checked against the server (login) 2 components to a form: The
HTML generating the form itself The server-side script that the form data is sent to (via GET or POST), taking care of the processing involved Server
should respond appropriately, redirecting the user to the appropriate destination or generating the appropriate page
Forms: client-side <html> <head> <title> A Form Example </title> </head><body> <form action="welcome.php" method="post"> Name: <br /> <input type="text" name="name" /><br /> Phone Number: <br /> <input type="text" name="phone" /><br /> <input type="submit" value="Submit"> </form> </body> </html>
form action – where to send the form data method – how to send the data (GET or POST) Name attributes become the keys used to access the corresponding fields in the $_GET or $_POST arrays
Forms: server-side <html> <head><title>This is welcome.php</title></head> <body> The name that was submitted was: &nbsp; <?php echo $_POST['name']; ?><br /> The phone number that was submitted was: &nbsp; <?php echo $_POST['phone']; ?><br /> </body> </html>
A simple PHP file that displays what was entered into the form
Can do many other things server-side depending on the situation
Note the use of $_POST
PHP Cookies and Sessions
Charles Liu
Cookies and sessions
HTTP is stateless – it does not keep track of the client between requests But sometimes we need to keep track of this information Shopping
cart “Remember me” on login sites
2 solutions to this issue Cookies
– small file stored client-side Sessions – relevant data stored on the server
Cookies
Cookies are stored on the user’s browser, and are sent to the server on every relevant request The $_COOKIE superglobal makes a cookie a keyvalue pairing Store
user information as a value with a known key Never assume a cookie has been set. Always check with isset($_COOKIE[$cookie_name]) before trying to use the cookie’s value
The setcookie() function
To set a cookie in PHP: setcookie(name, value, expire, path, domain);
Name and value correspond to $_COOKIE[$name] = $value
Expiration – cookie will no longer be read after the expiration
Useful to use time in seconds relative to the present:
Path and domain refer to where on the site the cookie is valid
time() + time in seconds until expiration
Usually ‘/’ for path and the top-level domain (yoursitename.com)
To delete a cookie, set a new cookie with same arguments but expiration in the past
Setting cookies
Cookies are set via the HTTP header Must
be sent before the body – before any HTML, CSS, JS, etc.
This code will not work: if(isset($_COOKIE["6470"])) { $value = $_COOKIE['6470']; echo "Cookie is set to $value"; } else { $value = 0; } // after echo statement: will not work! setcookie("6470", $value+1, time()+60*60);?>
Example of cookie usage
First visit: form with a text field for user’s name Subsequent visits: Welcome message with the name Store the name field in a cookie: Key:
“name”; value: the user’s name input into the form
Remember: when a cookie is set (the setcookie function call is made), the cookie can only be accessed on the next request
Contents of the HTTP request/response CLIENT
HTTP request: GET cookie.php HTTP reponse: HTML form
NO COOKIES
COOKIES SET
SERVER isset($_COOKIE[“name”])? NO isset($_GET[“name”])? NO respond with HTML form
HTTP request: GET name=“username” isset($_COOKIE[“name”])? NO isset($_GET[“name”])? YES set cookie on client HTTP response: set cookie welcome message based on user input HTTP request: cookie “name” = “username” isset($_COOKIE[“name”])? YES isset($_GET[“name”])? NO HTTP response: updated cookie update cookie on client welcome message based on cookie
Case 1: cookies already set if(isset($_COOKIE["name"])) { $cookie_exp = time()+60*60; // one hour $name = $_COOKIE["name"]; setcookie("name", $name, $cookie_exp); if (isset($_COOKIE["visits"])) { $num_visits = $_COOKIE["visits"]+1; setcookie("visits", $num_visits, $cookie_exp); } echo "Welcome $name! "; if (isset($_COOKIE["visits"])) { echo "You've visited $num_visits times"; } }
Cases 2&3: first and second visits // case 2: upon submission of form else if (isset($_GET["name"])) { $name = $_GET["name"]; setcookie("name", $name, $cookie_exp); setcookie("visits", 2, $cookie_exp); echo "Welcome $name! This is your second visit."; } // case 3: first visit: need to show form else { <form action="<?php $_SERVER["PHP_SELF"] ?>" method="get"> Enter your name here: <input type="text" name="name" /> <br /><input type="submit" /> </form> }
Sessions
Two main disadvantages of cookies Limited in size by browser Stored client-side can be tampered with
Sessions store user data on the server Limited only by server space Cannot be modified by users
A potential downside to sessions is that they expire when the browser is closed Sessions are identified by a session id: often a small cookie! But the rest of the data is still stored on the server
Using sessions
Call session_start() at top of every page to start session
Sets a cookie on the client: must follow same rules as cookies (before any HTML, CSS, JS, echo or print statements)
Access data using the $_SESSION superglobal, just like $_COOKIE, $_GET, or $_POST
<?php session_start(); if (isset($_SESSION["count"])) { $_SESSION["count"] += 1; echo "You\'ve visited here {$_SESSION['count']} times"; } else { $_SESSION["count"] = 1; echo "You\'ve visited once"; } ?>
Removing sessions
Remove an individual element of the $_SESSION superglobal unset($_SESSION[‘key_name’]); The
session still exists and can be modified.
Destroy the entire session, remove all data Use
the function session_destroy() $_SESSION no longer valid Will need to call session_start() to start a new session
Recap: a comparison COOKIES
SESSIONS
Where is data stored?
Locally on client
Remotely on server
Expiration?
Variable – determined when cookie is set
Session is destroyed when the browser is closed
Size limit?
Depends on browser
Depends only on server (practically no size limit)
Accessing information?
$_COOKIE
$_SESSION
General use?
Remember small things about the user, such as login name. Remember things after re-opening browser
Remembering varying amount of data about the user in one browsing “session”
PHP MySQL
Charles Liu
Databases and MySQL
Recall the basic reason for server-side programming We
need to store client data or look up data stored on the server
Databases give us an easy way to issue “commands” to insert, select, organize, and remove data MySQL: open-source database, relatively easy to set up, easy to use with PHP Other
SQL databases, as well as non-SQL options such as MongoDB
Connecting to MySQL
MySQL database server can contain many databases, each of which can contain many tables Connecting to the server via PHP: $db = mysql_connect(server, username, password); if (!$db) { // terminate and give error message die(mysql_error()); } mysql_select_db(database_name, $db);
$db is a database resource type. We use this variable to refer to the connection created
Making SQL queries
PHP function for making queries: mysql_query(query_string, db_resource);
Queries that return information, such as SELECT: returns a resource $result = mysql_query(query_string, $db);
In
this case, this resource is stored in the variable $result
Other queries, returns TRUE upon success. All queries return FALSE on failure. Best practice is to handle the error (e.g. die(mysql_error()))
Never trust user input
SQL injection
Attacker guesses the format of a query, then exploits If
the attacker is able to form a valid SQL query using one of the input fields, then there may be unintended results
Look at this code which simply displays the phone number given a correct username and password
SQL injection: example $db = mysql_connect("localhost", "6470user", "6470") or die(mysql_error()); mysql_select_db("6470example", $db) or die(mysql_error()); if (isset($_POST["username"]) && isset($_POST["password"])) { $user = $_POST["username"]; $pass = $_POST["password"]; $query = "SELECT PHONE FROM userinfo WHERE USER='$user' and PASSWORD='$pass'"; echo $query . "<br />"; $result = mysql_query($query, $db); $row = mysql_fetch_assoc($result); if ($row) { echo "Phone number is: {$row['PHONE']}"; } else { echo "Invalid user or password"; } }
SQL injection: example
The issue here is that we are “trusting” user input. What if the user inserts the string randompass’ OR ‘1=1
as the password? Resulting query: SELECT PHONE FROM userinfo WHERE USER=‘username’ and PASSWORD=‘randompass’ OR ‘1=1’
‘1=1’ always true. We can get the server to give the phone number regardless of username/password! Fix: must pass ALL user input through the function mysql_real_escape_string()
Retrieving information from a query ď&#x201A;¨
ď&#x201A;¨
Loop over the returned $result resource, row by row mysql_fetch_assoc() function: turns a row of the result into key-value pairs, where keys are the names of the fields and their values are the corresponding values in the table
$result = mysql_query(query, $db); while ($row = mysql_fetch_assoc($result)) { $col1 = $row['column_1_name']; $col2 = $row['column_2_name']; // and so forth... }
A registration-login example
Login page Check
username and password If already logged in (use sessions!), welcome the user by name Link to register page
Register page Form
for registration If registration is successful, confirm the username Link back to login page
Complete code can be downloaded from the video lectures website
A shared database resource
Both login and register pages use the same database connection Put database connection, select database code into the same file Reference the connection resource ($db) in other files
<?php $db = mysql_connect("localhost", "6470user", "6470") or die(mysql_error()); mysql_query("CREATE DATABASE IF NOT EXISTS 6470example") or die(mysql_error()); mysql_select_db("6470example", $db) or die(mysql_error()); mysql_query("CREATE TABLE IF NOT EXISTS users (USERNAME VARCHAR(2000), PASSWORD VARCHAR(2000))") or die(mysql_error()); ?>
The login page â&#x20AC;&#x201C; handle login request if (isset($_POST["username"]) && isset($_POST["password"])) { require("db.php"); // establish DB connection $user = $_POST["username"]; $pass = $_POST["password"]; $query = "SELECT PASSWORD from users WHERE USERNAME='" . mysql_real_escape_string($user) . "'"; $result = mysql_query($query, $db) or die(mysql_error()); $row = mysql_fetch_assoc($result); if ($pass == $row["PASSWORD"]) { $_SESSION["username"] = $user; } else { echo "Invalid username or password <br />"; } }
The register page if (isset($_POST["username"]) && isset($_POST["password"])) { require("db.php"); $user = mysql_real_escape_string($_POST["username"]); $pass = mysql_real_escape_string($_POST["password"]); $query = "INSERT INTO users VALUES ('$user', '$pass')"; mysql_query($query, $db) or die(mysql_error()); echo "Registration for $user was successful <br /><br />"; // HTML login <a href> tag } else { // HTML form }
MySQL recap
Connecting to database $db= mysql_connect(location, username, password) mysql_select_db(db_name, $db)
Making a query
Getting results of query
$result = mysql_query(query_string, $db) while($row = mysql_fetch_assoc($result))
Sanitizing user input
$username = mysql_real_escape_string($_POST[“username”])
PHP Conclusion
Charles Liu
What we’ve talked about…
Purpose of server-side programming Basic PHP syntax, arrays, functions Specifics to websites: cookies, sessions, HTTP requests and forms, MySQL Other server-side solutions: ASP.NET Python
PHP’s extensive documentation: http://www.php.net/manual/en
GOOD LUCK!